Generally, aqueous systems are kept sparkling clear (e.g. spa or swimming pool water) and uncontaminated by microbiological forms by a combination of the following:
maintaining the recommended level of disinfectant PA1 pH contol PA1 filtration PA1 maintaining proper chemical balance. PA1 X.sub.1, X.sub.2 =Cl, Br (any combination) PA1 1-chloro-5,5-dimethylhydantoin PA1 carbon dioxide PA1 nitrogen PA1 N-chloroisopropylamine PA1 chloride ion
Halogenated 5,5-dialkyl hydantoins have long been known to be effective as disinfectants for aqueous systems such as spas, swimming pools, and industrial recirculating waters etc. For spas and swimming pools, their use is illustrated in U.S. Pat. Nos. 3,346,446 and 3,412,021. Thus, included amongst halogenated 5,5-dialkyl hydantoins commonly used for combatting bacterial growth are 1,3-dichloro-5,5-dimethylhydantoin, 1,3-dibromo-5,5-dimethylhydantoin and mixed bromochloro hydantoins such as 1-bromo-3-chloro-5,5-dimethylhydantoin. Other halogenated 5,5-dialkyl hydantoins which can be used are dihalo derivatives of 5-ethyl-5-methylhydantoin, 5,5-diethylhydantoin, and the like together with blends of these various hydantoins. The phrase "halogenated 5,5-dialkyl hydantoin" as used herein is represented by the formula: ##STR1## wherein: R.sub.1, R.sub.2 =lower alkyl of 1 to 3 carbons
Occasionally, the disinfection process for aqueous systems may be overwhelmed for a variety of reasons - improper control of pH, level of disinfectant residuals, bather loading beyond the capacity of the disinfectant feeder in the case of pools or spas, equipment failure, inattention, etc. Under these circumstances, microbiological growth will proliferate. In the case of industrial systems, heat exchange efficiency may be drastically reduced. In the case of pool and spa systems the water becomes unsightly, and unsafe to use.
The conventional method of overcoming this problem, is to "shock" the system by increasing the free chlorine to a level as high as 5-15 parts per million (ppm), about 10 ppm being typical. The amount of chlorine added is a function of the total organic contaminants in the system. Chlorine is consumed in the degradation of these contaminants and when free and available chlorine is measurable most contamination is removed. At this point, additional chlorine is added to complete the decontamination process and affect disinfection. The final concentration (ppm) of free chlorine may vary from operator to operator, but is usually 5-15 ppm, more often about 10 ppm. In the case of a pool or spa, the free residual is then allowed to drop to less than 5 ppm before use. Thereafter, the pool or spa is usually maintained at about 0.5 to 1.5 ppm of halogen residual. Similar conditions apply to industrial recirculating systems. Thus, as used herein, the term "shocking" is intended to describe such a process. Chlorine sources such as hypochlorite salts, e.g., Ca(OCl).sub.2, NaOCl and the like, are commonly used for such shock treatment.
The use of halogenated 5,5-dialkyl hydantoins in aqueous systems such as a pool or spa will result in the slow buildup of residual partially halogenated or dehalogenated 5,5-dialkyl hydantoins in the system as the halogen is consumed in the disinfection process. It is of practical importance to determine how this residual halogenated 5,5-dialkyl hydantoin affects "shock" treatment of a pool. Petterson and Grzeskowiak in the Journal of Organic Chemistry, 24, 1414-1419 (1959), demonstrated that the initial product formed from 5,5-dimethylhydantoin and active chlorine is a monochlorodimethylhydantoin derivative, e.g.: ##STR2## The formation of the monochloro derivative removes the free chlorine in solution needed for disinfection. Further, the monochloro derivative shows minimal biological activity. The result is that the amount of chlorine needed to be added to attain the free chlorine level of about 10 ppm is greatly increased.
Satisfying the demand for chlorine also results in hydantoin ring-opening reactions. Petterson and Grzeskowiak studied the ring-opening reaction of 1,3-dichloro-5,5-dimethylhydantoin in dilute aqueous solutions over the pH range 3-12 and reported the following products:
We have also studied the hydrolysis of 1,3-dichloro-5,5-dimethylhydantoin and found that the products of hydrolysis were the same as those found by Petterson and Grzeskowiak with the exception that the product identified by Petterson as N-chloroisopropylamine is actually N-chloroisopropylimine. We have also found that similar chemistry applies for the 5-ethyl-5-methylhydantoin system. Therefore, the results described below for 5,5-dimethylhydantoin (DMH) system are applicable to 5,5-dialkyl hydantoin systems in general.
To illustrate how the halogenated 5,5-dialkyl hydantoins in aqueous solution affect shock treatment, a series of experiments were carried out varying the the levels of both dimethyl hydantoin (DMH) and chlorine added to solution at pH 7.5 and 40.degree. C. (spa conditions). The data given in Table I illustrates that residual DMH leads to the following results:
(1) DMH is converted to monochloro DMH (based on the observed difference between free and total chlorine levels),
(2) ring-opening reactions take place, generating N-chloroisopropylimine and acetone,
(3) high levels of hypochlorite are required to attain the desired free chlorine level of about 10 ppm: 20 ppm of residual DMH requried 45 ppm of hypochlorite, and 40 ppm of residual DMH requried 69 ppm of hypochlorite.
TABLE I __________________________________________________________________________ Shock Treatment of Halogenated 5,5-dialkyl Hydantoin Solutions Chlorine.sup.2 Moles Chlorine.sup.2 N--chloroiso- DMH.sup.1 added per mole Chlorine.sup.2, ppm propylimine Acetone Solution ppm ppm DMH Free Total ppm ppm __________________________________________________________________________ A 0 10 -- 8 10 .sup. NM.sup.3 NM B 20 10 0.92 0.4 7 .sup. ND.sup.4 ND C 40 10 0.46 0.4 7 ND ND D 100 10 0.18 0.8 8 ND ND E 20 20 1.83 1.5 12 2.2 1.1 F 40 20 0.92 0.9 16 ND ND G 100 20 0.37 0.8 16 ND ND H 20 30 2.75 2.2 12 3.8 1.5 I 40 30 1.37 1.2 16 2.1 1.1 J 100 30 0.55 1.2 26 ND ND K 20 45 4.1 12 26 5.2 2.4 L 40 69 3.1 10 26 9.4 2.2 __________________________________________________________________________ .sup.1 DMH = 5,5dimethylhydantoin .sup.2 HOCl added, expressed as available chlorine (Cl.sub.2) .sup. 3 NM = Not Measured .sup.4 ND = Not Detected
While not wishing to limit the present invention, we believe that the acetone results from hydrolysis of a portion of the N-chloroisopropylimine: ##STR3## We have also found that ketones are present in aqueous systems disinfected with HOCl in the absence of halogenated 5,5-dialkyl hydantoin disinfectants from the oxidation of organic substances by active halogen, and thus are not associated only with hydantoin-based disinfectants.
The N-chloroisopropylimine is, however, specific to the DMH system. N-chloroisopropylimine is a material that consumes active halogen in being generated, is not microbicidally active, has a sharp, halogen-like odor, is an irritant, and is toxic.
Overall, then, it is a general object of the invention to provide a process which prevents the formation of the toxic N-chloroimines and hydantoin ring-opening by-products thereby minimizing user risks in such applications as spas and pools.
It is a further object of the invention to provide a process which will repress the formation of monochloro-5,5-dialkyl hydantoins which cause lower biological activity and whose toxicity is unknown.
It is a further object of the invention to provide a process which optimizes the efficient utilization of chlorine by reducing undesirable by-product formation.
A further object of the invention is to provide a shock treatment where the amount of chlorine necessary to shock the pool is reduced.